1. Field of the Invention
The present invention relates to an ink jet printing system and a method provided with an ink-jet print head for discharging ink by generating bubbles with the application of thermal energy.
According to the present invention, the term xe2x80x9cprintingxe2x80x9d or xe2x80x9cprintxe2x80x9d means that not only figurative or meaningful images such as characters and figures, but also nonfigurative images or images that do not communicate meaning such as patterns are formed on printed media.
Further, the term xe2x80x9cprinting apparatusxe2x80x9d or xe2x80x9cprinterxe2x80x9d used in the following description of the specification indicates an ink jet printer.
2. Description of the Related Art
Conventionally, there has been known as an ink jet printing method, a so-called bubble jet printing method, which applies thermal energy to ink in each of ink flow paths in a printing apparatus such as a printer to generate a bubble. As a result, the ink is discharged from each of discharge ports by an abrupt volumetric change associated with the formation of the bubble. A droplet of ink discharged is made to adhere to the surface of a printed medium so that an image will be formed thereon. One of the printing apparatuses using the above-mentioned bubble jet printing methods is disclosed in U.S. Pat. No. 4,723,129. This patent teaches a bubble jet printing apparatus, which is typically provided with discharge ports for discharging ink, liquid flow paths communicating with the respective discharge ports, and electrothermal converting elements arranged in the respective liquid flow paths as energy generating means for discharging the ink.
This type of printing method enables the printing apparatus to print out high-quality images at high speeds and low noise levels. In addition, a print head using this type of printing method arranges discharge ports in a compact apparatus more densely, which makes it easy to obtain a high-resolution printed image even though it is a color image. Thus, since the bubble jet printing method has lots of advantageous points, it has recently been employed for not only many office equipment, such as printers, copiers and facsimiles, but also industrial systems such as apparatuses used at printworks.
As the application of bubble jet technology expands to a wide range of products, various demands for the technology have been increasing through the years.
For example, to obtain a high-quality image, proper driving conditions have been proposed so that they can realize an ink discharging method capable of discharging ink properly at high speed under the influence of stable bubble generation. Further, from the high-speed print""s point of view, improvements in the shape of a liquid flow path have been proposed to obtain an ink-jet print head capable of speeding up a refill of ink into the liquid flow path from which an amount of ink has been discharged.
It has conventionally been known that the front portion of a bubble generated by film boiling (of an edge shooting type) has a major impact on discharging of ink, but no attention is paid to a technique for efficiently using this portion to form discharged droplets. The inventors have carefully studied to solve technical problems on this matter.
Paying attention to the relationship between displacement or deformation of a movable member and generation of a bubble, the inventors acquired the following findings.
One of the findings is that a stopper can control the displacement of a free end of the movable member relative to the growth of a bubble. The stopper restricts the displacement of the movable member, which in turn restricts the growth of the bubble on the upstream side of the liquid flow path to transmit energy to the downstream side on which the discharge port is formed, thereby efficiently discharging ink.
The above-mentioned ink-jet print head discharges ink droplets nearly in the form of liquid columns with bulb-like tips at the instant of discharging the ink from the discharge ports due to generation of bubbles, respectively. The same phenomenon happens to a conventional head structure, but the ink-jet print head having such a movable member displaces or deforms the movable member in the process of growing a bubble. Then, when the movable member thus displaced comes in contact with the stopper, a substantially closed space is formed in the liquid flow path except the discharge port. Since the closed space is maintained until the bubble disappears and hence the movable member is separated from the stopper, energy generated by bubble disappearance serves as such a force as to move ink near the discharge port in the upstream direction. As a result, an ink interface or meniscus is rapidly pulled into the liquid flow path from the discharge port just after the bubble disappearance is started. Then, a tail portion connected with a discharged droplet outside of the discharge port to form part of a liquid column is cut off in a flash by a strong pulling force of the meniscus. This makes it possible to minimize generation of a satellite particle formed from the tail portion, and hence improve print quality.
Although the meniscus is rapidly pulled in, this phenomenon does not continue to pull the tail portion, which prevents reduction in the discharging speed. Further, since distance between the discharged droplet and the satellite particle becomes short, the satellite particle is attracted to the discharged droplet by means of so-called slipstream behind the discharged droplet. As a result, the discharged droplet and the satellite droplet could become united, which makes it possible to reduce image quality degradation.
To make image quality higher, the ink-jet print head having the above-mentioned movable member is further required to reduce image quality degradation caused by satellite droplets conspicuous at single-dot printing. In carefully studying this matter, the applicant acquired the following novel knowledge:
1. It is essential to manage or control physical properties of ink such as viscosity and surface tension, reduction in design flexibility such as a layout of the head nozzles or driving method, and a manufacturing tolerances.
2. Many satellite droplets tend to take place unevenly in only one direction, not in all scanning directions of a carriage.
The present invention has been made in view of the above-mentioned facts, and an object thereof is to provide ink jet printing system and method capable of reduce the degradation of printed images due to satellite droplets.
In attaining the above-mentioned object and according to the present invention, there is provided an ink jet printing system constituted of an ink jet printing apparatus and a printer driver. The ink jet printing apparatus includes an ink jet head from which ink is so discharged that an image will be printed out on a recorded medium, conveying means for conveying the recorded medium, and a holding means for keeping the ink jet head reciprocating in the main or horizontal scanning direction intersecting the conveying direction of the recording medium. The printer driver creates image information in an information processing apparatus on the basis of density information. The ink jet printing system according to the present invention comprises image information detecting means and image information changing means. The image information detecting means receives first image information to detect whether the first image information represents an image prone to significant degradation due to detrimental effects of satellite dots. The image information changing means changes information to be used, if it is detected that the first image information represents an image prone to significant degradation due to detrimental effects of satellite dots, from the first image information to second image information representing an image less influenced by the satellite dots than the first image information.
In the above-mentioned configuration of the ink jet printing system, when printing is to be made on the basis of the first print information on a single-dot print tending to generate satellite dots, only main droplets are discharged with adding the second print information continuously to the discharge of the main droplet based on the first print information. The second print information is information for generating not satellite dots. In this case, the changing means changes the print information composed of the first print information alone into the print information composed of the first print information and the second print information. In other words, main droplets discharged on the basis of the second print information are hit on respective satellite dots alighted adjacent to but slightly spaced with the main droplets discharged on the basis of the first print information, which makes the satellite dots inconspicuous.
The ink-jet print head may have a heating element for generating thermal energy to generate a bubble in an ink flow path. Alternatively, the ink-jet print head may have a movable member with a free end provided in a bubble generating region in the ink flow path communicating the discharge port, and displaced or deformed with the growth of the bubble.
According to the present invention, there is also provided an ink jet printing method for creating image information from density information, driving an ink jet head on the basis of the image information, and discharging ink to a recorded medium so that an image will be printed on the recorded medium. The ink jet printing method comprises the following two steps: one receiving first image information to detect whether the first image information represents an image prone to significant degradation due to detrimental effects of satellite dots, and the other changing image information to be used, if detected that the first image information represents an image prone to significant degradation due to detrimental effects of satellite dots, from the first image information to second image information less influenced by satellite dots than represented by the first image information.
In the above-mentioned ink jet printing method, two or more ink dots are continuously discharged in a continuous discharging process, which can reduce image quality degradation resulting from generation of satellite dots, especially noticeable in single-dot printing. The continuous discharging process may be carried out on a printer driver side in a host computer, or on the ink jet printing apparatus in which the inkjet print head is mounted.
The ink jet printing method may further comprising the step of creating print data indicative of an arrangement of continuous pixel data in the main or horizontal scanning direction, where each pixel corresponds to each dot hit on the printed medium.